Rapid, precise measurement of the position and orientation of a tool or workpiece is critical to many automated manufacturing processes. Although a variety of different measurement systems have been developed, optical measuring systems have proven precise, adaptable, reliable, and relatively inexpensive.
Most optical measuring systems exploit various effects obtained by manipulating the output of low-intensity lasers. For example, highly accurate linear distance measurements can be obtained by counting interference fringes that shift position as a laser beam reflects from a shifting target. Such a system may be initially calibrated by measuring the time of flight of a laser pulse that strikes a target and returns to a source.
Orientation measurements have posed more of a challenge, since, for example, a light beam parallel to a rotational axis of a target may register no distance variation. One solution to this problem utilizes the polarizing effects of a Glan-Thompson prism, which resolves an incoming laser beam into two orthogonal vector components that vary in intensity according to the rotational orientation of the prism with respect to the beam. Once such a system is calibrated, a target's angle of rotation about an axis may be calculated from the measured intensity differential between output vector components.
However, obtaining complete positional data for a target using the simplest forms of such measurement techniques may require a separate distance-measuring system for each translational axis and a separate rotation-measuring system for each rotational axis. As the setup and operation of simple multi-dimensional measurement systems may become cumbersome and expensive, it is highly desirable to make as many different but simultaneous measurements as possible with a single light beam.